The present invention relates to refrigeration systems, and, more particularly, it relates to a method and apparatus for controlling removal of heat from the condenser of a mechanical refrigeration system, particularly but not exclusively a liquid chiller refrigeration system.
Large capacity, liquid chiller, refrigeration systems typically employ multiple fans for removal of heat from the high temperature side of an operating system or from the condenser or cooling tower of such a system. The amount of heat removal is usually determined by the number of the multiple fans that are operated at one time, but may be varied by speed control of one or more of the fans, or in other ways that provide for variable circulation of a cooling medium past the relatively hot refrigerant in the condenser or water in the cooling tower. Moreover, the amount of heat removed from the high temperature side of a refrigeration system has an effect on the operating efficiency of the overall system under differing operating conditions.
Conventional fan controllers control the fans based on the discharge pressure and temperature of the system compressor and/or ambient air temperature. Conventional controllers also shut down the entire refrigeration systems, when certain safety conditions are sensed. Use of such limited operating parameters and controls, however, frequently leads to inefficient and unsteady operation of the condenser or cooling tower fans.
To achieve the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed to a method and system for controlling the cooling of refrigerant in the condenser, to maximize efficiency and safety. In a preferred embodiment, the method and system controls the cooling of refrigerant in the condenser and/or the expansion valve position.
The invention includes a refrigeration system that circulates a refrigerant through a closed loop having a high pressure side extending from a compressor, though a condenser, to a flow-restricting expansion device, and a low pressure side extending between the expansion device, through an evaporator, to the compressor. The invention further includes a variable capacity cooling system to cool refrigerant in the condenser and a controller to monitor pressures associated with the high and low sides of the system, wherein the controller adjusts the variable capacity cooling system to lower the pressure associated with the high side of the system by increasing cooling of refrigerant in the condenser toward or at the maximum level, while maintaining an acceptable pressure differential between the high pressure side of the system and the low pressure side of the system. Under the invention, the controller also can monitor other conditions, such as superheat or liquid content of the refrigerant proximate the inlet of the compressor, to maintain an acceptable amount of superheat in the refrigerant applied to the compressor, and/or ensure that liquid refrigerant is not applied to the compressor.
In another aspect, the advantages of the invention are achieved and the purpose thereof is served by a method for controlling a refrigeration system that circulates a refrigerant through a closed loop having a high pressure side extending from a compressor, through a condenser, to a flow-restricting expansion device, and a low pressure side extending between the expansion device, through an evaporator, to the compressor, the method including monitoring system pressure on the high side and low side of the system, monitoring superheat of the refrigerant in the low pressure side of the system, and periodically increasing cooling of the refrigerant in the condenser toward the maximum possible level as long as the superheat of the refrigerant in the low pressure side of the system exceeds a minimum threshold value and a refrigerant pressure differential between the high and low pressure sides of the system exceeds a minimum threshold value. In a similar fashion, the method can include monitoring the pressure of oil applied to a compressor, the superheat, or liquid content of refrigerant, and periodically increasing the cooling of the refrigerant, as long as one or both of these monitored conditions does not exceed an acceptable level.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.